Telephone trunk circuit



Feb. 9 1926. 1571,966'

A. J. RAY

TELEPHONE TRUNK CIRCUIT Filed Sept. '7, 1925 5 Sheets-Sheet 1 Imrsn ur flFl'hur J. Hay

Feb. 9,192e.. I 1,571,966

' A. J. RAY

TELEPHONE TRUNK CIRCUIT Filed Sept. '7, 1923 5 Sheets-Sheet 2 Y Imreu ur- Feb. 9 1926. 1,571,966

- A. J RAY TELEPHONE TRUNK CIRCUIT Filed Sept. '7, 1925 3 Sheets-Sheet 5 Patented Feb. 9, 1926.

UNITED STATES.

PATENT OFFICE.

ARTHUR J. BAY, OF CHICAGO, ILLINOIS ASSIGNOB, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

TELEPHONE TRUNK CIRCUIT.

Application filed September 7, 1923. Serial No. 661,366.

'ln all whom it may concern:

Tie it known that l, A n'rnvn J. RAY, a citizen ol' the United States of America, and a resident of Chicago, Cook County, and Stale of Illinois, have invented certain new and useful Improvements in Telephone Trunk (ircuits of which the following is a specification.

The present invention relates in general to telephone trunk circuits and is particularly useful in connection with such trunk circuits as areadapted for use in interconnecting otfices of widely separated automatic and manual exchanges.

The principal object of the invention is to provide circuit arrangements whereby, without resorting to the usual equipment, such as composite coils, composite ringing apparatus, etc., two two-way trunk circuits between a switchboard of a manual exchange and an automatic exchange maybe phantomed to provide an additional one-way circuit from the automatic exchange to a switchboard at the, manual exchange.

A further object is to provide a trunking scheme adapted for use in conjunction with a group of the above type trunks which permits the number of connections which can be extended from the manual exchange to equal, on an average, the number of connections which may he'extended from the automatic to the manual exchange regardless of the fact that the phantom trunks are only one-way trunks.

The drawings, comprising Figs. 1 to 3, imi-lusive, when laid out from left to right in the order-named, show two physical circuits extending between an automatic and a manual exchange, having a phantom trunk circuit superimposed thereon.

Referring more in detail to each figure separately, Fig. 1 shows two line switches C and C, each individual to its respective repeater R and B (Fig. 2). These line switches are of the well known rotary type and have access to called lines in the automatic ofiice, by way of the usual switch train used in that office by calling subscribers to complete connections to other subscribers in that ofliee. The selector E is of the well known Strowger type, is accessible to subscribers of the automatic exchange, and may be controlled by such subscribers to complete connections, to the manual exchange. Une level of the bank contacts accessible to the selector E is shown to better enable applicant to illustrate the trunking arrangement used.

Fig. 2 shows two two-way repeaters R and R and a ring down repeater R The circuits of repeaters It and It will be fully described hereinafter. The circuits of repeater R are also shown in full, but since this repeater is identical to the repeater R a detailed description of repeater R will not be necessary. The outgoing conductors of the repeaters R, R and R terminate in their respective repeating coils RC, RC and RC (Fig. 3).

Fig. 3 shows the repeating coils of physical trunks X. and Y and the repeating coils of the phantom circuit superimposed thereon. This figure also shows the manual equipment into which these trunks terminate, and the necessary equipment'for controlling automatic switches by way of the trunklines X and Y. The repeating coils shown in the left portion of Fig. 3 and all equipment shown in Figs. 1 and 2 is in the automatic oflice, while the equipment at the right of Fig. 3 is in the manual oflice.

, In order to describe the operation of the invention, it will first be assumed that a subscriber in the automatic exchange desires to extend a connection to some subscriber in the manual exchange. The calling subscriber upon removing his receiver causes the line switch associated with his line to ex tend the connection to an idle selector switch. It is assumed that in the present case the selector E is the switch seized. Accordingly, the line and release relays 8 and 9 are energized in the usual manner. Relay 9 upon operating, at its upper armature, applies ground to the release conductor to maintain the line switch of the calling line in operated position, and at its lower armature prepares the usual operating circuit for series relay 22 and vertical magnet 21. The

calling subscriber may now operate his calllng device in accordance with the digit required to step the wipers of the selector E opposite the level of bank contacts in which s rin 13 are closed and a circuit is comp e for stepping relay 23 by way of interrupter springs of the rotary magnetl i, off normal springs 13, and the working contact of the lower armature of series relay 22 and said armature to the grounded con ductor 15. Relay 23, upon operating, at its lower armature prepares an initial operating circuit for the rotary magnet 14, and at its u per armature completes a locking circuit fliritself independent of series relay 22. At the termination of the vertical movement of the switch, series relay 22 deenergizes and at its lower armature completes a circuit for the rotary magnet which, upon operating, moves the wipers of selector E into engagement with the first set of bank contacts of the selected group, and near the end of its stroke also interrupts the previously described locking circuit of stepping relay 23. Relay 23 upon dcenergizing, at its lower armature, opens the circuit of the rotary magnet, which also dcenergizes. It will be assumed in the present case thatthe trunk line terminating in the first set of bank contacts engaged by the wipers of selector E is idle at this time. Switching relay 10, which was previously short circuited by the operated relay 23, now energizes over a circuit extending from grounded conductor 15, winding of said switching relay, off normal springs 13, interrupter springs of the rotary magnet, and the winding of stepping relay 23 to battery. The resistance of switching relay 10 is very high compared to that g of stepping relay 23, and this latter relay is,

therefore, not energized at this time. Switching relay 10, however, operates and at its armature 16 applies ground to the test wiper 18 which, in turn, applies ground to test contact 19 to make this trunk line busy to other selectors such as the selector E, at its armature 26 opens a point in the operating circuit of release magnet 27. and at its armatures 11 and 12 disconnects line relay 8 from in bridge of conductors 28 and 29 and connects these conductors to conductors 73 and 74: across which are bridged the windings of line relay 61 of the repeater R. It will be noted that when ground was applied to the test contact 19 by the operation of the switching relay, a circuit for slow release relay 60 was also completed. Relays 60 and 61 operate. Relay 60 at its armature 68 completes a circuit for slow release relay 71. This relay in turn operates and at its armatures 69 and 70 connects ringing current to conductors 73 and 74. Relay 61, upon operating, at its armatures 64: and 65 closes normally open points in conductors 73 and 74, and at its armature 63 completes a circuit for slow release relay 62. Relay 62, upon operating, at its armature 66 opens the circuit of slow release relay 60 and at this same armature and its working contact applies ground to conductor 20 to revent the release of the selector E and t e line switch of the calling line by the deenergization of slow release relay 9 of the selector E. Belay 60, upon deenergizing, opens the 7 circuit of relay 71, which latter relay disconnects generator from conductors 73 and 74 and closes points opened in these- (onductors when ringing current was applied. By the operations above described, it will be seen that a short ringing current impulse is transmitted by way of condm-iors 73 and 74: to the left hand winding of repeat ing coil B0. A similar current impulse is, therefore, induced into the right hand winding of repeating coil BC. This latter or induced current flows by way of conductors and 80, upper and lower right hand windings of repeating coils RC and R0 conductors of trunk lines X and Y, left hand upper and lower windings of repeating coils RC and RC, conductors 82 and 82, and the left hand windings of repeating coil BC. This ringing current impulse is repeated into the right hand windings of repeating coil RC, across which is bridged the drop 86 at a manual operators position causing this drop to operate.

Attention is called to the fact that a small portion of the ringing current transmitted out over conductor 80 flows by way of eonductors 89 and 90 in parallel, through springs controlled by reversing relay 50, armatures 46 and/l7 and their resting contacts, and the upper and lower windings of impedaiu e coil 12 and line relay 40 in parallel to the grounded battery, thence by way of the windings of line relay 40 and impedance coil 42 in parallel, conductors 89' and 90, in parallel, conductor 80, and the right hand windings of the repeating coil RC back to conductor 80. It will be noted that the current flow through the windings of line relays 40 and 40 in this circuit is in such a direction that these windings oppose each other. In other words, these windings are connected differentially with respect to this particular circuit. therefore, not operate over this circuit. The inclusion of these relays in the circuit above described ordinarily would shunt an appreciable amount of ringing current from the left hand windings of the repeating coil RC but this is prevented by use of the impedance coils 42 and 42'. These impedance coils are so connected that their windings are cumulative in this circuit, and therefore build up sufiicient impedance to prevent any appreciable amount of ringing current being shunted from the repeating coil RC.

Returning to the description of operation: The manual operator upon observing .the operated condition of drop 86 responds by means of a suitable cord circuit, and after ascertaining the subscriber wanted com- These relays Will,

plates the connection in any well known manner.

When the conversation has been complet ed, the calling subscriber, by replacing his receiver, causes the dcenergization of line relay 61 of repeater R -Relay 61, upon retracting its armature 63, opens the circuit of slow release relay 62, and at this same armature com letes an operatin circuit for relay 71, whi circuit is opene an instant later by the deenergization of slow relay 62. Relay 62 at its armature 66 removes ground from conductor 20, causing the selector E and the line switch of the calling line to restore to normal in the usual and well known manner. The momentary energizetion of slow release relay 71 causes a ringing current impulse to be transmitted over the previously described circuit, which is effective to operate a ring up relay in the operators cord which was substituted for the drop 86 when the operator responded. The operation of this latter relay com letes a circuit for the usual disconnect sig'na thereby notitying the operator that the calling subscriber has terminated the conversation. The operator upon withdrawing her cord from the jack J causes the drop 86 to be again connected in bridge of the repeating coil RC. All of the relays in the repeater R haying now been restored to normal and ground having accordingly been removed from the test contact 19, the phantom trunk line is now in readiness to be again taken for use.

Taking particular notice ofthe arrangement of connections on the bank contacts of selector E, it will be noted that the first three sets of contacts of the group will have phantom trunks associated therewith, while the remaining seven sets of contacts will have physical trunks associated therewith. It will be seen that in this way the greater portion of the physical circuits ordinarily will be accessible for use in extending connections from the manual oflice.

It will now be assumed that a connection is being set up by a subscriber in the automatic office at atime when all the phantom trunks are busy. Under these conditions when the test wiper 18 of the selector E engages test contact 19, grolmd will be present thereon and a. new circuit is completed for the steppPng relay 23 extending by way of grounded wiper 18, armature 16 and its resting contact, ofl:' normal springs 13, interrupter springs of the rotary magnet, and the winding of stepping relay 23 to battery. Relay 23 upon oper ting again completes the circuit of rotary magnet 14, which again onergizes, moving the wipers of the selector E into, engagement with the next set'of bank contacts. As soon as the rotary magnet 14, deenergizes a circuit is again completed for relay 23 by Way of its interrupter springs and wiper 18 and the next busy test contact. Relay 23 therefore again operates to 14. This alternate operation of stepping relay 23 and rotary magnet 14 will continue until an ungrounded test contact'is found. It is assumed that the first idle trunk line of the group is the'physical trunk line terminating in the fourth set of bankcontacts of the selected level, in which terminate the conductors 5, 6 and 7 of the two-way reseater The stepping relay 23 therefore eenergizes and swltchin relay 10 operates in the manner previous y described, this time substitutin the windings of line relay 56 for the windings of the line relay 8. Line relay 56 therefore operates, at its armature 30 completes a circuit for the reversing relay 50, at its armature 59 completes a circuit for slow. release relay 31, and at its armatures 57 and 58 disconnects the line switch C from connection with conductors 53 and 54 and connects these conductors to conductors 5 and 6 which now extend to the calling line. Relay 31, upon operating, at its armature 32 applies ground to conductor 7 to prevent the release of selector E and the line switch of the calling subscribers line, as previously described. Relay 50, upon operating, reverses the connection of the conductors 89 and 90 with respect to relay 40 for a purpose which will subsequently be made clear.

It will be noted that prior to the energization of slow relay 31 a circuit is completed for slow relay 43, by way of conductor 7, armature 32 and its resting contact, and armature 39 and its resting contact. Relay 43, upon operating, completes a circuit for slow relay 45, which in turn operates, at its armatures 46 and 47, momentarily dis connecting rela 40 and the impedance coil 42 from in bri ge of conductors 89 and 90, and at its armatures 48 and 49 momentarily connecting ringing current in bridge of conductors .93 and 94. It will be evident that the relays 43 and 45 of the repeater B. have the same function as the relays 60 and 71 of the, repeater R. The ringing current impulse transmitted over conductors 93 and 94 to the left hand winding of repeating coil RC is repeated by the right hand windings of the repeating coil, over conductors 91 and 92 to the left hand windings of repeating coil RC Where it is again repeated by the right hand winding of the repeating coil to the drop 77, which operates. The operator, upon noting the operated condition of drop 77, responds by inserting a. plug of one of her cords in the jack J. This results in the opening of contacts 97, thereby opening the circuit of the drop 77. Springs 76 are also closed when the plug is inserted in the jack J, causing the vpolarized relay 78 to be bridged across conductors 95 and 96 which extend by way of the left hand upper and again complete a circuit for rotary magnet lower windings of repeating coil RC to conductors 91 and 92. Conductors 91 and I 92 extend by way of the upper right and lower right hand windings of repeating coil RC, conductors 89 and 91), working contacts of armafures 72 and 73 and the said armatures, armaturcs ll and i? and their resting contacts to the windings of in'ipedance coil 42 and line relay 41) to battery and ground respectively. Line relay 49 operates, at its armature 7i closes a normally open point in talking conductor 54 and at its arn'laiure 41 completes a circuit for slow release relay 37. Relay 3? upon operating, at armature 39 completes a circuit for the polarizing winding of relay iii, and at armature 38 closes a point in the operating circuit of slow relay 51. Relay 3% will operate only when current flow is in the proper direction in both of its windings and is therefore not operated at this time. Since the reversing relay 50 in the repeater R has been operated, current flow is in the wrong direction to cause the operation of polarized relay 78 at this time. The operator after ascertaining the party desired now completes the connection in any well known manner.

At the termination of the conversation, when the calling subscriber replaces his receiver on the switchhook, the line and release relays 5G and 31 deenergize. The deen ergization of relay 56 causes ground to be removed from the reversing relay,which also deenergizes, reversing the current flow in conductors 91 and 92 back to normal. Polarized' relay 78 now operates, causing the disconnect lamp L to glow to indicate to the operator that the calling subscriber has terminated the conversation. Relay 31, upon deenergizing, removes ground from conductor 7, permitting the selector E and the line switch of the calling line to be restored to normal in the manner previously described. The operator upon noting the lighted condition of lamp L withdraws the plug of her cord from the jack J, thereby opening the circuit of line relay 40 and polarized relay 78 again connecting the drop 77 in bridge of the conductors extending from the right hand windings of the repeating coil RC. Relay 78, upon deenergizing, causes lamp L to be extinguished. Relay 40, upon deenergizing, at its armature 74 opens a point in conductor 54, and at its armature 41 opens the circuit of slow release relay 37, and, prior to the release of this latter relay, at its resting contact, completes a momentary circuit for relay 51. The operation of relay 51, however, is without effect since contacts 74: are open at this time.

It will now be assumed that the operator in the manual oflice desires to extend a connection to some subscriber in the automatic ofiice. The operator proceeds by inserting a plug of her cord circuit into jack J, bringing about the previously described disconnection of drop 77 and the bridging of polarized relay 78 across conductors 89 and 90. Line relay 40 operates over the previously described circuit, at its armature 41 completes a circuitfor slow release relay 3?. and at its armature 74 closes a normally open point in conductor 54. Relay 37 upon operating, at its armature 39, opens a point in the operating circuit of slow relay 4-3, at this same aruuiture applies ground to the test contact ll of the selector E to make this trunk line busy to subscribers of the automatic oliice, and at its armature 36 closes a bridge across conductors 53 and 54:. This bridge extends from conductor 53, resting contact of armature and the said armature, armature 52 and its resting contact, conductor 93, upper left hand winding of repeating coil RC, conductor 87, lower windiug of electropolarized relay 34, Working contact of armature 36 and the said armature, armature 33 and its resting contact, conductor 88, lower lci't hand winding of re peating coil RC. conductor 94, resting contact oi armature 55 and the said armature, armature 4S) and its resting contact, armature 74 and its working contact, to conductor 5%. Relay S7, at its armature 39, also completes a circuit for the upper winding of the. olectropolarized relay 34. The current flow through the windings of relay 34 is in such a direction that the windings oppose each other, and this relay does not operate at this time. The closure of the above described bridge causes the line switch 0 to operate to select an idle trunk line. When an idle trunk line is found, the switching relay 2 of the line switch G operates and extends the conductors 3 and 1- to conductors terminating in a selector switch having access, by way of the usual switch t'ain used, to subscribers in the automatic exchange. The operator in the manual office now ope ates her calling device key K, substituting the calling device S or the polarized relay 7S, and proceeds to operate the .alling device S in accordance with the digits of the called subscribers number. The line relay -10 dcenergizes each time the springs of the calling device are opened. Upon the first retraction of armature 41. of the line relay 40, a circuit is completed for slow release relay 5]. This relay upon operating closes a direct bridge across conductors 53 and Each time springs 74 of the line relay 40 are opened the line relay of the selector seized also retracts its armature, causing that selector to be operated in the same manner as was the selector E to select a desired group of selectors or connectors depending on the size of the exchange. hen the. complete number has been set up by the operator, the operator again inserting the polarized relay 78 in bridge of the trunk line.

Since the current flow in conductors 91 and 92 has not yet been reversed the polarized relay operates causing lamp L to glow. When the called subscriber responds, the

' back bridge relay of the connector switch used reverses the direction of current flow in conductors 53 and 54. Electropolarized relay 34 now operates and at its armature 35 completes a circuit for the reversing relay 50. Relay 50, upon operating, reverses the current flow in conductors 91 and 92, cansingthe polarized relay 78 to deenergize and extinguish the lamp L to notify the operator that the called subscriber has re sponded.

At the termination of the conversation when the called subscriber replaces his receiver on the switchhook, electropolarized relay 34 deenergizes, causing the reversing relay 50 to also deenergize. This latter rclay, upon deenergization, again restores the normal current flow in conductors 91 and 92, thereby causing polarized relay 78 to again operate and complete a circuit for the lamp L, which now glows to indicate to the operator that the called subscriber has replaced his receiver. This time when the operator withdraws the lug of her cord circuit from the jack J, line and release relays 40 and 37 deenergize, thereby opening the bridge extending across conductors 53 and 54. The line switch C and the other switches used in the connection now restore to normal in the usual manner. The deenergization of slow release relay 31 causes'ground. to be removed from the test contact 11 in the bank of the selector E and its multiples,

making this trunk line again accessible to.

subscribers in the automatic oflice.

It will be readily appreciated that the impedance coils 42 and 42' are not onl of utility in preventing ringing current rom being shunted from repeating coil RC of the phantom trunk, as hereinbefore explained, but are also efl'ective to prevent the shuntin of the talkino' currents.

Applicant believes that the use of loop dialling circuits on physical trunks which have phantom trunks superimposed thereon is broadly new, and this feature will therefore be so claimed.

What is claimed:

1. In a telephone system a trunk line interconnecting two exchanges, a switch controlling relay responsive to interruptions in a closed direct current circuit including both conductors of said trunk line in series, a second trunk line identical to the first, and a phantom trunk line superimposed on the conductors of both of said trunk lines.

2. In a telephone system, a pair of trunk lines interconnecting an automatic and a manual exchange, automatic switches in said automatic exchange, two switch control circuits, one including the two conductors of one of said trunk lines in series and the other including the two conductors of the other of said trunk lines in series, a battery in the automatic exchange common to both said circuits, and a phantom trunk line superimposed on said pair of trunk lines.

3. In combination, two switch controlling circuits, each including a double wound line relay and a double wound impedance coil so connected that the impedance coil windin-gs are differentially connected while the line relay windings are cumulatively connected, a phantom circuit including the windings of both of said line relays and said impedance coils in such a manner that the windings of said impedance coils will be cumulatively connected, and the windings of the relays differentially connected. I

4. In a telephone system, a group of trunk lines comprising two physical and one phantom trunk, a repeating coil in the phantom trunk, a relay and an impedance coil in series with the two conductors of each of the physical trunks and operable thereover to control automatic switches, said relays and impedance coils being connected in multiple with windings of said repeating coil, the windings of said impedance coils and line relays bein differentially and cumulatively connecte respectively, in the switch control circuits, while being cumulatively and difi'erentially connected, respectively, in the phantom circuit.

5. In a telephone system, a manual and an automatic office, one way phantom trunk lines and two way physical trunk lines infor use only in extending connections from the automatic-office, and means for making the one way trunks first choice to automatic switches in the automatic oflice.

6. In a telephone system, one and two way trunk lines extending between two oiiices, each one way trunk line being superimposed on two of said two way trunk lines, automatic switches at one of said oflices having access to said trunk lines to complete connections to the other oflice, and a trunking arrangement making the one way trunks first choice to said automatic switches.

7. In a telephone system, two oflices, a number of one and two way trunks interconnecting said ofiices, one ofiice having all of said trunks accessible thereto for extending connections to the other oflice, the other 'olfice having only a portion of said trunks accessible thereto for extending connections to said first oflice,and means for preventing the first oflice from using trunks accessible to the other oflice while any of the not accessible to the other ofice are 8. In a telephone system, two parallel physical trunk lines, a phantom trunk line superimposed on said trunk lines, a line re ay at one end of one physical trunk line controlled over the two-conductors thereof in series, a second line relay at the same end of the other hysical trunk line and controlled over the two conductors thereof in series, a common battery in series with both lino relays, and impedance coils connected in series with said line relays to prevent the same from shuntin currents away from the phantom trunk inc.

9. In a telephone system,- an automatic switch of the type whichv restores its wipers to normal after each connection, a plurality of physical trunk lines connected to bank contacts of said switch, and a plurality of phantom trunk lines connected to bank contents of said switch which are closer to the normal position of said wipers than said first mentioned bank contacts.

10. In a telephone system, a plurality of physical trunk lines, a pluralit of phantom trunk lines superimpose on said physical trunk lines, an automatic hunting switch, sets of bank contacts assigned to said phantom trunk lines and accessible to said switch as first choice, and other sets of bank contacts assigned to said physical trunk lines and accessible to said switch as second choice.

11. In a telephone system, a pair of trunk lines interconnectin two exchanges, automatic switches in t e first exchange, two switch control circuits, one including the two conductors of one of said trunk lines in series and the other including the two conductors of the other of said trunk lines in series, a batter in the first exchange common to both said circuits, a phantom trunk line superimposed on said pair of trunk lines, and means for preventin currents from belng shunted awa from sai phantom trunk line through sai battery.

12. In a telephone system, a air of trunk lines interconnectin two excianges, automatic switches in t e first exchange, two switch control circuits, one includlng the two conductors of one of said trunk lines in series and the other including the two conductors of the'other of said trunk lines in series, a battery in the first exchange common to both said circuits, a phantom trunk line superimposed on said pair of trunk lines, and coils inserted in each of said control circuits at points outside the phantom, said coils being difierentially wound with respect to currents in the control circuits but onmulatively wound with respect to currents shunted away from the phantom trunk line.

13. In a telephone system, a' trunk line connecting an automatic exchange with a manual exchange, means including automatic switches in the automatic exchange for completing connections over said trunk line originating at either exchange, a polarized relay at the manual exchange individual to said trunk line, a supervisory signal controlled by said relay, and a reversing relay individual to the trunk line at the automatic exchange operated automatically in both automatic to manual and manual to automatic calls for reversin the direction of current flow in said trun line to actuate said relay when the automatic subscriber involved hangs up his receiver.

In witness whereof, I hereunto subscribe iny name this 4th day of September, A. D.

ARTHUR J. RAY. 

